Since its inception, Radiation Oncology, more than any other cancer treatment discipline, has considered the late effects of therapy on normal tissues and organs. The disparity between the intensity of acute and late effects and the inability to predict the eventual manifestations of late normal tissue injury has made practicing radiation oncologists recognize the importance of careful patient follow-up. Not only do early somatic functional and structural alterations occur during the actual treatment itself, but late effects manifest months to years after acute effects heal, and often progress with time. A recommendation of a uniform system is the desired end product based upon 'consensus criteria.' In September 1985, an NCI Consensus Conference on toxicity was held in Baltimore, MD. A subcommittee, comprised of representatives from several cooperative groups was formed at this meeting with the aim of addressing the question of standardized toxic effects criteria. Most of these recommendations were put into effect in the Common Toxicity Criteria (CTC) first distributed by NCI in 1988. What remains to be done is to devise additions to the CTC for subacute and chronic (late) toxicities from combined modality treatment strategies which include radiotherapy. The purpose of this Late Effects Conference will be analyze the current scoring system for acute and late effects and develop a system which embodies simplicity of design and will result in accuracy of detail. The Conference will concern itself specifically with the development of scoring systems to be used in all sites and to recommend methods to validate them. This could be achieved through development of longitudinal studies of the dose-limiting normal tissues or organs to be conducted in cooperative group settings. The conference participants will assume the responsibility of moving these recommendations and methods into the appropriate cooperative group with which each may be affiliated. While the development of studies for interventions to ameliorate acute and prevent late effects will be one of the desired ends this is beyond the scope of this Conference.